1. Technical Field
The present invention relates to an image display apparatus.
2. Related Art
Recently, utilization of a laser beam source as a high-output light source has been expected with development of a high-output semiconductor laser and a blue semiconductor laser. The laser beam source has advantages such as excellent color reproducibility, easy and instant lighting, and long life. Laser beams generally used are beams having equalized phase and high coherence (highly coherent beams), and having uniform polarization directions on the cross section perpendicular to the center axis of the beams (oscillation directions of the electric fields of the beams) such as linear polarized lights and circular polarized lights.
On the other hand, laser beams having non-uniform polarization directions different from known laser beams having uniform polarization directions described above are attracting attention. The laser beams having non-uniform polarization directions are vector beams, for example.
The vector beams are axially symmetric polarized lights having spatial polarization distribution. It is known that the vector beams have various types of polarization oscillation conditions (modes) in accordance with solutions for formulas expressing the vector beams. For example, primary vector beams are known as axially symmetric polarized laser beams having “optical vortex” as a point of zero optical field intensity at the center of the center axis of the beams. In recent years, the method for producing the vector beams has been widely investigated so as to effectively utilize the special polarization characteristics of the vector beams (for example, see JP-A-2008-216641). For example, a method for utilizing the vector beams as a light source of an optical memory device has been proposed (for example, see JP-A-2006-48807).
Since application and development aimed at utilization of laser beams having uniform polarization directions have been chiefly studied, most of technologies currently used are assumed to use laser beams having uniform polarization directions. Thus, utilization of laser beams having non-uniform polarization directions such as vector beams is not sufficiently developed, and application of this type of laser beams capable of providing characteristics different from those of the laser beams traditionally used is expected.
In addition, a projector (image display apparatus) including a laser beam source has been developed in recent years. This type of projector having a narrow wavelength range of the laser beam source can provide a sufficiently wide color reproducibility range, and thus can reduce the size of the apparatus and the number of included components. Accordingly, the projector including the laser beam source has the high potential of playing a role as a projector for the next generation.
However, in case of the projector which uses the laser beams having uniform polarization directions for display, a phenomenon called speckles occurs in some cases. When the speckle phenomenon is caused, bright points and dark points are distributed in a striped pattern or a spot pattern due to light coherence caused by a scattering body such as a screen.
Speckles are regarded as a factor causing adverse effects such as scintillating effect, and thus make an observer uncomfortable during observation of image display. Since the laser beams having uniform polarization directions have high coherence and easily produce speckles, an appropriate technology for removing speckles is essential for using these laser beams as the light source.
For reducing speckles, such a method is known which produces plural patterns of speckles by using lights having low coherence (incoherent lights) such as lights having slightly different wavelengths, and overlaps the plural speckles at a time to make the patterns of the speckles unrecognizable. This method overlaps speckles produced by two types of polarized lights and equalizes the speckles to reduce the speckle phenomenon.
In case of an image display apparatus including a self-light-emission-type display element, however, light emitted from the display element forms an image as pixels of a display image on a screen, and thus lights emitted from plural light sources of the display element do not overlap with one another. Accordingly, in case of the image display apparatus which includes the self-light-emission-type display element and uses the ordinary laser beams, speckle reduction cannot be sufficiently achieved even when the laser beams emitted from the plural light sources have low coherence between one another.